1. Field of the Invention
The present invention relates to low light level detection and imaging devices and more particularly to a photon sensing and counting device for image detection. It has applications in photomultiplier tubes (PMT), image intensifier tubes and solid state imaging sensors.
2. Description of the Background Art
References relating to the technology of photosensor devices using amorphous Selenium for charge multiplication are as follows.
U.S. Pat. No. 5,466,613 issued Nov. 14, 1995 to Andoh et al. entitled METHOD OF MANUFACTURING A CAMERA DEVICE and U.S. Pat. No. 5,399,882 issued Mar. 21, 1995 to Andoh et al. entitled CAMERA DEVICE AND METHOD OF MANUFACTURING THE SAME disclose a camera device having favorable multiplication characteristics (quantum efficiency) as well as improved sensitivity in a visible light region (especially the region on the red side) and a method of manufacturing the same are provided. The camera device includes a hole injection stop layer, a first photoelectric converting layer including selenium, a second photoelectric converting layer having spectral sensitivity characteristics which are different from those of the first photoelectric converting layer, a third photoelectric converting layer including selenium, and an electron injection stop layer. As a result, it is possible to improve multiplication characteristics (quantum efficiency) and to improve the sensitivity in the visible light region (especially the
U.S. Pat. No. 5,101,255 issued Mar. 31, 1992 to Ishioka et al. entitled AMORPHOUS PHOTOELECTRIC CONVERSION DEVICE WITH AVALANCHE discloses a photoelectric conversion device which comprises: a photoconductive layer made of amorphous semiconductor material which shows charge multiplication and which converts photo signals into electric signals; and a substrate having electric circuits or the like (for example switching elements) for reading the electric signals. The amorphous semiconductor material used according to the invention shows the charge multiplication action under predetermined intensity of electric field so that a high sensitive photoelectric conversion device having a gain which is not smaller than 1 is realized.
U.S. Pat. No. 4,952,839 issued Aug. 28, 1990 and U.S. Pat. No. 4,888,521 issued Dec. 19, 1989 to Tanioka et al. entitled PHOTOCONDUCTIVE DEVICE AND METHOD OF OPERATING THE SAME discloses a photoconductive device having a photoconductive layer which includes an amorphous semiconductor layer capable of charge multiplication in at least a part thereof is disclosed. The method of operating such a photoconductive device is also disclosed. By using the avalanche effect of the amorphous semiconductor layer, it is possible to realize a highly sensitive photoconductive device while maintaining low lag property.
U.S. Pat. No. 4,900,975 issued Feb. 13, 1990 to Shimomoto et al. entitled TARGET OF IMAGE PICKUP TUBE HAVING AN AMORPHOUS SEMICONDUCTOR LAMINATE discloses a target of an image pickup tube is formed by laminating at least a transparent conductive film, an amorphous layer consisting essentially of silicon, and an amorphous layer consisting essentially of selenium in the above order on a light-transmitting substrate.
U.S. Pat. No. 4,883,562 issued Nov. 28, 1989 to Ogawa et al. entitled METHOD OF MAKING A PHOTOSENSOR discloses a method of making an image pickup tube target using an amorphous photoconductive layer. When an electrode, an amorphous semiconductor layer; etc. are provided on a substrate, the steps of ion etching away a surface of the substrate and forming the electrode are performed so that a target is produced in which no defects are substantially caused in a reproduced image even in a high electric field is applied across the target.
U.S. Pat. 4,701,394 issued Oct. 20, 1987 to Inoue et al. entitled IMAGE FORMING MEMBER FOR ELECTROPHOTOGRAPHY discloses an image-forming member for electrophotography comprises a photoconductive layer including as constituting layers, a hydrogenated amorphous silicon layer and an amorphous inorganic semiconductor layer. The amorphous inorganic semiconductor layer is laminated on the hydrogenated amorphous silicon layer to thereby provide a heterojunction.
At present, the state of the art in low light level imaging is based on image intensifier tubes followed by a tapered fiber optic face plate followed by a charge coupled device array to image the output screen. To achieve the resolution required of such a system is very costly and its performance under bright light leaves a lot to be desired.
The present invention provides an improved solid state imager or vidicon type tube with higher sensitivity and wider spectral band to enable more cost effective and higher performance TV sensors to be achieved. Broadening the spectral band of image pick up tubes and solid state image sensors allows the detection of objects that a human eye can not see. This is achieved by adding infrared and ultraviolet absorbers ahead of an avalanche multiplying layer and injecting excited hole type mobile carriers into the a-Se avalanching layer.